How can i come back in shape post delivery, without exercises?

Hi, i am due this march with my third baby. Before conceiving my weight was 78 kgs (height 5,6), obviously overweight, but please give me tips to reduce my weight soon after my delivery, as i ume that it is easy to loose weight and regain our shape at this time. Also, What diet is best which can help me tuck in my stomach as well. I am really concerned. please help!!!!